An image forming apparatus—such as a photocopier, a printer, and a facsimile—uses a developer, such as a toner, to develop an image. Generally, in such an image forming apparatus, a developer container such as a toner cartridge is provided. The developer container contains (stores) the developer, and supplies the developer to a developing section of the image forming apparatus during development.
Incidentally, in recent years, there has been a demand for an image forming apparatus which can print a large amount of documents at high speed. For example, there is such an image forming apparatus (the type that can form images on 50 or greater sheets of paper for one minute) that can handle 999 sheets at a time. Further, the image forming apparatus occasionally carries out a continuous printing for over 999 sheets, depending on a setting of the printing. Therefore, such a fast image forming apparatus needs a toner cartridge that can contain a large amount of toner, and some toner cartridges can contain, for example, approximately 1400 g of toner.
Disclosed in Japanese Laid-Open Patent Application Tokukaihei 08-339115/1996 (published on Dec. 24, 1996; hereinafter, referred to as “Reference 1”) is a specific example of a toner cartridge (supplying developer container) that can contain a large amount of toner. FIG. 25 is a perspective view illustrating the supplying developer container 20 described in Reference 1. The supplying developer container 20 has a cylindrical shape whose ends are closed, and has a containing space for toner. The supplying developer container 20 includes supplying means (first protruding ledge) 21a, and supplying means (second protruding ledge) 21b. The supplying means 21a inwardly protrudes in a radial direction of the supplying developer container 20, and spirally extends, from a first end portion 20a of the supplying developer container 20 to a central portion 20c of the supplying developer container 20, with respect to an axis line L20, the first end portion 20a being one end in the axis line L20, and the central portion being in a center of the axis line L20. Meanwhile, the supplying means 21b inwardly protrudes in the radial direction of the supplying developer container 20, and spirally extends, from its second end portion 20b to its central portion 20c, with respect to the axis line L20, the second end portion being the other end in the axis L20. In the central portion 20c of the supplying developer container 20, an outlet hole 22 is formed. The outlet hole 22 penetrates the supplying developer container 20, and connects the containing space to an outside of the supplying developer container 20.
The supplying developer container 20 is coupled with an image forming apparatus main body (not shown) so that the axis line L20 is parallel to a horizontal direction, and that the central portion 20c is positionally associated with a toner supplying hole (not shown) which is provided in the image forming apparatus main body, the toner supplying hole being open upward. The supplying developer container 20 is driven, to rotate around the axis line L20, by a driving section provided on the image forming apparatus main body. By doing this, the toner contained in the containing space is sent to the central portion 20c by the supplying means 21a and 21b. When the outlet hole 22 comes to a position to face the toner supplying hole, the toner is supplied, via the outlet hole 22, to the toner supplying hole.
As described above, the supplying developer container 20 of Reference 1 contains toner, and rotates to supply the toner to the outlet hole 22 by the supplying means 21a and 21b, both of which extend to the outlet hole 22. Thereafter, the developer thus supplied is discharged from the outlet hole 22, thereby supplying the developer to a developing apparatus (not shown) provided in the image forming apparatus. Therefore, if the supplying toner container 20 is provided in the image forming apparatus so that the outlet hole 22 can be disposed above the toner supplying hole which supplies the toner to the developing apparatus, a space that is not efficiently used is reduced. Accordingly, the supplying developer container 20 can contain larger amounts of toner.
However, it is difficult to attain a complete seal between the image forming apparatus main body and the central portion 20c that rotates. Accordingly, when the supplying developer container 20 rotates, the toner possibly leaks from a space between the central portion and the image forming apparatus main body, and possibly flies about inside the image forming apparatus main body.
Further, a toner is a fine particle having a particle diameter of 4 μm to 10 μm, and is highly flowable. Therefore, in cases where the rotation of the supplying developer container 20 is stopped when the outlet hole 22 faces the toner supplying hole, a large amount of toner possibly flows into the toner supplying hole via the outlet hole 22. When the toner is over supplied from the toner supplying hole to the developing section, toner density in the developing apparatus is increased at the time of the oversupply. This possibly causes images to be unevenly developed.
Further, under the supplying developer container 20, the developing apparatus is provided. Therefore, due to a load (i.e. weight of the toner) imposed on the toner, the toner flows into the developing apparatus via the outlet hole 22. Accordingly, depending on the load imposed on the toner (i.e., amount of toner left in the supplying developer container 20), an amount of the toner to be supplied is varied. This leads to unstable supply of the toner to the developing apparatus.
Specifically, when a large amount of the toner is contained in the supplying developer container 20, a heavy load is imposed on the toner, thereby increasing the amount of the toner to be supplied to the developing apparatus due to its weight. Further, in this case, the toner density increase due to pressure caused by its weight, and the amount of toner per unit volume becomes too large. As a result, the amount of the toner to be supplied is further increased. However, as the toner in the supplying developer container 20 decreases, the load imposed on the toner (i.e. the weight of the toner) decreases. This decreases the amount of the toner to be supplied to the developing apparatus. Further, because the toner as a result becomes less dense, and the amount of the toner per unit volume is reduced, the amount of the toner thus supplied is further reduced.
The supplying developer container 20 described in Reference 1 has such a problem that the amount of the toner to be supplied depends on the amount of the toner contained in the supplying developer container 20, and that the toner is therefore unstably supplied. When the toner is thus unstably supplied, images are not always evenly developed, thereby deteriorating image qualities. Further, when the amount of toner remaining in the supplying developer container 20 is small, the toner cannot be reliably supplied to the developing apparatus. A sensor, which detects how much toner is left, would possibly misunderstand that there is no toner left in the supplying developer container 20, and accordingly causes a message to be displayed advising to change the supplying developer container (toner cartridge), even when sufficient toner is still left in the supplying developer container 20.